1. Field of the Invention
The subject invention relates to a brake rotor assembly for a disc braking system of a vehicle, and further relates to a method of producing the brake rotor assembly.
2. Description of the Prior Art
Disc braking systems for vehicles utilize a brake caliper to urge a pair of brake pads into frictional engagement with a brake rotor (brake disc) to provide a braking force to the vehicle. In order to increase the braking force applied by the disc braking system, it is known to incorporate a second brake rotor into the disc braking system. This may be referred to as a dual disc braking system. The dual disc braking system necessitates that a first brake rotor be slideable along a central axis relative to a second brake rotor. The first brake rotor slides over and rotates with a hub (wheel end or axle). The slideable first brake rotor compensates for wear in the brake pads over time. Accordingly, as the brake pads wear, the first brake rotor slides over the hub along the central axis to compensate for the wear in the brake pads. The slideable first brake rotor typically includes teeth extending inwardly from an inner periphery of the first brake rotor toward the central axis. The teeth are disposed radially about the central axis for engaging channels in the wheel hub for transmitting rotational movement therebetween. The teeth may be integrally cast with the first brake rotor. Typically, the brake rotor and the teeth are cast integrally together from a grey cast iron. However, the grey cast iron tends to fracture under certain high stress braking conditions and high thermal loads generated by the frictional engagement between the brake pads and the brake disc. Additionally, the grey cast iron tends to corrode at the toothed engagement between the teeth of the brake rotor and the groove in the hub, thereby bonding the brake rotor to the hub.
Alternatively, as disclosed in U.S. Pat. No. 4,540,067 (the '067 patent), the first brake rotor may be an assembly wherein an annular ring forms the teeth and is attached to a friction disc by a plurality of bolts. This type of assembly is often referred to as a composite brake rotor. The composite brake rotor, as assembled in the '067 patent, utilizes a portion of the friction disc to attach the annular ring thereto, thereby reducing a contact area between the brake pads and the friction disc and reducing the braking force provided by the disc braking system.
U.S. Pat. No. 5,109,960 (the '960 patent) discloses a method of producing a composite brake rotor. The method includes casting a hub to include a supporting ring extending radially outward from the hub. The hub is bolted to a wheel end, but is not slideable thereon. The supporting ring includes depressions extending across the supporting ring. The hub is placed in a mold, with a pair of parallel friction discs then being cast around the hub. The pair of friction discs include a plurality of webs extending therebetween. The plurality of webs interlock with the plurality of depressions in the supporting ring to interlock the friction discs and the hub. The hub is preferably cast from grey cast iron.
U.S. Pat. No. 5,823,303 (the '303 patent) also discloses a composite brake rotor. The brake rotor of the '303 patent includes a hub having a plurality of pins extending outwardly away from a central axis and disposed radially about the hub. The hub is bolted to a wheel end, but is not slideable thereon. A friction disc is cast around the hub, with the plurality of pins in interlocking engagement with the friction disc. As disclosed in the '303 patent, the hub and the plurality of pins may be integrally cast from gray cast iron. Alternatively, the hub may be formed from steel. When the hub is formed from steel, the plurality of pins may be formed from a high grade steel, such as stainless steel, and connected to the hub by welding or bonding.
Accordingly, there remains a need for a brake rotor suitable for use in a dual brake disc system having a plurality of teeth of sufficient strength to resist fracture while maximizing the contact area between the brake pads and the friction disc.